Hijackers may have sent coded messages on Internet
Carl T. Hall, Chronicle Science Writer Friday, October 12, 2001
As White House officials warned that Osama bin Laden may be sending secret
coded messages to his followers through videotaped statements, federal
investigators are checking into the possibility that the Sept. 11 hijackers
did the same thing on the Internet.
Law enforcement specialists say that terrorists have been using hidden
messages in computer files for years. In past investigations, encrypted
messages have been ferreted out from files deep within password-protected
"You have to go through multiple layers," said former FBI agent Clint Van
Zandt, now head of a Virginia consulting firm that advises corporate clients.
"First, you have to get the computer, then get into the hard drive, then you
have to look at each document and see what's behind the veil. It could be in
the header, the footer, in pictures -- just about anything can have messages
concealed in it."
Security experts said the latest software, which can be readily downloaded
from the Internet, makes it a simple matter to pass around messages in digital
images and other files that can be attached to e-mail or loaded onto a Web
K.J. Kuchta, a specialist in computer forensics in Phoenix, Ariz., and
chairman of an information-technology security council of the American Society
for Industrial Security, counted at least 28 message-hiding software packages
available as freeware or shareware.
"There are legitimate uses for it," he said, notably in the area of preventing
copyright infringement by planting a hidden brand in a data file. "But it's
something law enforcement is really going to have to focus on."
Scanned photographs can even be spiked with code, printed out and mailed or
hand-carried to a recipient, who then rescans the image to pull out the
message. Messages can also be inserted into video or audio files.
Secret writing has been used to thwart enemies since at least the fifth
century B.C., the most famous example being that of the Greek Histaiaeus, who
is said to have written a message -- urging revolt against the Persian king --
on the shaved head of an aide, who was sent on his way only after the hair had
The modern form of this ancient hidden-writing technology is known as digital
watermarking or "steganography." Although it was developed for legitimate
commercial purposes, it has become a growing concern for those trying to
thwart the communications systems of global terrorism networks.
"If you want to tell someone to go blow something up, this is an easy way to
accomplish that," said Scott Craver, an electrical engineer at Princeton
University writing his Ph.D. dissertation on the forensic analysis of hidden
The latest steganography software requires virtually no special skill for
anyone with access to a computer linked to public networks. "Even the most
elaborate techniques can be embedded in a computer program and executed just
by pressing an 'OK' button," Craver said.
Perpetrators of the Sept. 11 atrocity are said to have used computers in
public libraries to stay in touch, although an FBI spokeswoman yesterday would
not comment on any details of the investigation so far.
Just about any data file can be used, said Edward Delp, a steganography expert
and professor of electrical and computer engineering at Purdue University in
West Lafayette, Ind.
"You type in your e-mail, attach an image, and to the average person it looks
like I just sent you a picture," he said. "You don't necessarily have to be a
rocket scientist to do this."
However, there are standard ways to screen files in order to determine if they
are clean, the same way computer users rely on software to check for worms and
viruses in e-mail attachments. So-called "steganalysis" software can be used
to hunt quickly for telltale statistical clues -- "digital fingerprints" -- of
These may be more or less obvious depending on the size of the message, the
size of the file in which it is carried -- and the sophistication of the
"A lot of people are trying to break these steganographic systems," Delp said.
"Some are quite easy to break, some are not. It can be done but the techniques
are not perfect."
Of course, message-hiding can be readily combined with encryption so that even
if a message is unearthed, it may be difficult to read accurately. And even if
a message is unscrambled its true meaning may be clear only to those who know
a prearranged code word or image.
Technology can also be used to blur the message, adding some electronic noise
to a data file that allows a sender to "kind of spread the message out over
the image, which makes it a lot harder to detect," Delp said.
What may appear to an outsider as nothing but static might actually be a
hidden note, which can be read only by someone running the data file through
the right filter.
--- --- --- --- ---
Useless hypotheses, etc.:
consciousness, phlogiston, philosophy, vitalism, mind, free will, qualia,
analog computing, cultural relativism, GAC, Cyc, Eliza, cryonics, individual
uniqueness, ego, human values, scientific relinquishment
We move into a better future in proportion as science displaces superstition.
This archive was generated by hypermail 2b30 : Sat May 11 2002 - 17:44:13 MDT